Thermal relay



B. w. JONES THERMAL RELAY Aug. 18, 1936.

Filed Dec. 29, 195

a e w m a NE a w n 4 5 w 0 Z IU 1 .m C H W e.m.. k i nn mm s w 1P 4 n w M M, H B 5 3 g b Patented Aug. 18, 1936 UNITED STATES PATENT OFFICE 2,051,319 THERMAL RELAY.

New York Application December 29, 1934, Serial No. 759,718

20 Claims.

My invention relates to protective devices or relays, more particularly to thermal overload relays, and has for an object the provision of a simple and reliable overload relay of this type.

Various types of thermal overload relays have heretofore been proposed for protecting electrical energy translating apparatus such as motors, transformers and the like from overload conditions which subject the component parts of the apparatus to dangerous temperatures. In

applying thermal overload protection to apparatus of this type, it is often desirable and sometimes necessary to immerse the overload relay in a body of oil. For example, it is often necessary to locate an electric motor in a hazardous place which is exposed to explosive or corrosive atmospheres, and it is essential in installations of this type that the entire control, including the overload relay, be immersed in oil. Also, in applying thermal overload protection to an oil-cooled.

transformer, it is desirable that the thermal overload relay be immersed in the body of oil which surrounds the windings of the transformer.

The immersion of the thermal overload relay in a body of oil gives rise to serious operating difliculties, due principally to the fact that when known types of thermal overload relays designed for operation in air are immersed in oil, the normal current rating of the relay may be doubled or more than doubled by the thermal effect of the oil on the relay parts. Such a differential between the normal current-rating of a relay when operated in air and when operated in oil is highly undesirable, and considerable need has been found 3 for a thermal overload relay which is satisfactory for oil immersed operations.

In motor applications, such as described above, it is desirable that the thermal relay shall be substantially unaffected by the temperature of the oil bath, and in a transformer installation,

it is desirable that the temperature of the immersing oil shall have substantially the same cooling effect upon the relay as it has upon the transformer windings and core. Accordingly, it

is a further object of my invention to provide a thermal overload relay of simple construction, the operation of which is independent of ambient temperature conditions to a predetermined degree.

In carrying out my invention in one form, I provide a thermal overload relay comprising a sealed envelope or container of thermal insulating material disposed adjacent an energizing winding adapted to be connected in circuit with the apparatus to be protected. Within the sealed envelope I provide a closed circuited secondary winding in inductive relation with the energizing winding and a thermo-responsive device intimately thermally associated with the closed secondary winding to be influenced by the heat gen- 5 erated in the secondary winding, the walls of the envelope serving thermally to isolate the enclosed parts.

The sealed envelope is evacuated to a predetermined degree of vacuum, depending upon the 10 purpose for which the relay is to be employed. That is, if it is desirable that the relay shall be substantially independent of ambient temperature conditions as in the motor application suggested above, a very high vacuum should be 15 employed, so as substantially to eliminate heat transfer between the relay parts and the ambient oil by conduction, or convection. If it is desirable to utilize the relay in an application, such as the transformer application referred to, in 20 which the relay should be affected to a predetermined degree by ambient temperature conditions, the sealed envelope may be only partially evacuated or may contain an inert gas of suflicient pressure so that the thermal effect of the ambient 25 temperature will affect the relay parts in the same degree as the operating parts of the protected apparatus are aifected.

More particularly, the operating parts of the relay enclosed within the envelope comprise a 30 magnetic core surrounded by a single-tum secondary winding such as a cylindrical conductor, and a'bimetallic element secured at one end to the cylindrical conductor, the other end of the bimetallic element being arranged to control a 35 pair of circuit controlling contacts. Suitable control circuit leads extend from the contacts through the walls of the sealed envelope and are hermetically sealed therein.

For a more complete understanding of my in- 4 vention, reference should .now be had to the drawing, in which Fig. l is an elevational crosssectional view of a portion of a thermal relay embodying my invention; Fig. 2 is a perspective view of a relay embodying the device shown in 45 Fig. l, certain parts being broken away; Fig. 3 is a somewhat diagrammatic view of the relay immersed in a body ofjpil; and Fig. 4 is a partial cross-sectional view of another modification of the device shown in Fig. 1. 50

Referring now to Figs. 1 and 2 of the drawing,

I have shown a thermal overload relay comprising a sealed envelope or container I0 preferably formed of glass or similar material having thermal insulating properties, within which is ar- 55 ranged a magnetizable core structure comprising an axially extending rod or bolt ll supporting a magnetizable body comprising a spirally wound strip l2 of magnetizable material, such as iron, and a pair of spaced cup-shaped magnetizable members [3 and Hi. It will be observed that the supporting bolt i 8 extends through suitable apertures in the cup-shaped members l3 and M and that the upper end of the bolt threadedly engages one end of a metallic supporting member E5, the other end of which is suitably fastened by spotwelding to a pair of supporting wires it sealed in a wall of the envelope Ill. The other end of the a washer i8 whereby the bolt serves to maintain the spirally wound strip l2 and the cup-shaped members l3 and M in assembled relation. Secured to the cup-shaped member M is a leafspring [9 arranged to engage a wall of the envelope It! so as to position the lower end of the core structure relative to the envelope.

Surrounding the spirally wound portion l2, I provide a heating member comprising a cylinder 20 of copper or other suitable conducting material which serves as a closed circuited single-turn winding. The upper end of the cylinder 28 is arranged tightly to engage an enlarged shoulder portion 2! formed on the spirally wound portion l2 in order to provide good thermal conductivity between the core structure and the heating member, and a bimetallic element ,22 is directly secured at one end thereof to the lower end of the cylindrical conductor 20 in heat-receiving relation therewith. It will be observed that the fixed end of the bimetallic element 22 is electrically connected to the lower end of the bolt H by-an L-shaped conductor 23 which extends through a suitable slot 2-3 in the cup-shaped member M, and that the upper end of the bimetallic element 22 extends into a similar slot 25 in the cup-shaped member'l3 and carries a contact 26 normally engaging a cooperating contact 2'5.

The cooperating contact 27! is supported on one end of a spring arm 28, the other end of which is arranged between a conducting block 29 and a pair of insulating washers 33 supported adjacent the supporting member l5 by means of a pair of screws 3| and 32. An insulating block 33 is provided, as shown, electrically to insulate the supporting member 55 from the screws Sfl and 32 which threadedly engage the block 29 and serve to maintain the block and the washers 30 in tight engagement with the spring arm 23 fixedly to secure one end thereof. It will be seen that the screw 32 extends outwardly from the block 29 through an aperture 36 in the spring arm 28 adjacent its free end and is provided with a headed portion 35 to form an adjustable stop for the spring supported contact 2'21.

In order that the contacts 26 and 2t may be electrically connected in an external control cirbimetallic element 22, the contacts 26 and 2?, the

spring arm 28 and the conducting block 23 to the conducting lead 37.

aosne'ze Any suitable energizing means may be provided externally of the sealed envelope in for producing an alternating flux in the magnetizable core structure within the envelope in order to induce a heating current in the single-turn secondary 20. 6 In the arrangement shown in Fig. 2, the sealed container I0 is disposed in suitable apertures 38 and 39 in the opposite sides of a. laminated magnetizable frame All which is secured to a suitable base member H. As will be seen, the lower end of the container it rests on a bracket 42 the opposite ends of which are respectively connected to the base M and to the frame ML-the bracket 42 being so spaced relative to the frame 40 as to support the container at in a position in which the cup-shaped members l3 and I4 within the container are respectively adjacent the opposite sides of the frame 40 whereby the frame provides a plurality of low reluctance, magnetic return paths for the core structure within the envelope. A 20 suitable supporting strap 43 having its respective ends connected to the base member 4! is provided for securely holding the upper end of the container m.

Surrounding the portion of the envelope or container H] which extends between the sides of the frame 40, I provide a spool M of insulating material on which is wound an energizing winding 45 for producing a magnetic flux in the frame 40 and in the magnetizable core structure within the container W. In some cases it may be desirable to omit the magnetic return paths constituting the frame 40, in which case satisfactory operation of the relay may be obtained merely by increasing the ampere turns in the energizing winding 45, the necessary ratio of increase being in the neighborhood 015-221.

It will be apparent now that I have provided an improved thermal relay in which the thermal operating parts are thermally isolated by the walls of the envelope ll! so as to be independent of external ambient temperatures to a degree which depends upon the character of the ambient medium within the envelope. The relay is suitable for operation either in air or in an immersing fluid, and in Fig. 3 I have shown somewhat diagrammatically an arrangement in which the base member M of the relay is secured to a wall 46 of a. tank or casing which contains a body of oil 41.

When my improved thermal relay is to be employed for protecting'an energy translating apparatus such as a motor or a transformer, the energizing winding 45 is connected in circuit with the apparatus to be protected and the lead-in conductors 36 and 31 of the relay are connected 5 in circuit with a suitable control device, such as the trip coil of a circuit breaker, arranged to deenergize the apparatus to be protected when the normally closed relay contacts 26 and 21 move to open circuit position. With the energizing winding 45 so connected and normal currents flowing in the protected apparatus, a magnetic fiux will be set up in the magnetizable core structure comprising the spirally wound portion l2 and the cup-shaped members l3 and I4 which will induce a heating current in the closed circuited secondary 20. It will be remembered that the portion of the closed circuited heating mem ber 23 which engages the shoulder portion 2| is intimately thermally related to the magnetizable 70 core structure which serves also as a heat storage body and under normal current conditions the heat generated in the secondary member 20 will be conducted to the magnetizable core structure of the relay and will be dissipated therefrom by 75 radiation to the walls of the envelope Ill. The degree of vacuum in the envelope l6 and the proportions of the magnetizable core structure are such that with normal load current a state of equilibrium exists in which the rate of heat dissipation is equal to the rate of heat generation and consequently, the bimetallic element 22 will not be affected sufliciently to separate the contacts 26 and 21.

Upon the occurrence of a predetermined overload current condition in the apparatus to be protected, the secondary currents induced in the closed circuited winding 26 and the heat generated thereby will be so increased as to cause the bimetallic element 25 to flex by reason of the heat conducted thereto from the heating member It will be apparent that as the bimetallic element 22 is heated the contact 26 carried by the free end thereof will move to the right as shown in Fig. 1 and that the spring supported contact 21 will follow the movement of the contact 26 until the spring arm 28 engages the head 35 on the screw 32. Continued movement of the, contact 26 to the right will then be effective to open the circuit between the contacts 26 and 21, the position of the screw 32 relative to the contact arm 28 determining the point at which the relay contacts will open.

In Fig. 4 I have partially shown a modified relay which difiers from the device shown in Fig. 1 only in the arrangement for supporting the magnetizable structure and the circuit controlling contacts within the enclosing envelope. The portion of the device which is not shown is identical with the arrangement shown in Fig. 1 and similar reference numerals refer to similar parts in the two modifications.

In this modification of the relay the supporting rod or bolt H threadedly engages a cup-shaped magnetizable member 48 which corresponds to the cup-shaped member l3 shown in Fig. 1. Secured to a wall of the cup-shaped member 48 as by the screws49 is an insulating block 50 which in turn is fastened as by the screws 5| to a supporting member 52 of conducting material, the upper end of which is secured as by spot-welding to supporting wires 53 sealed in a wall of the container 10. In this arrangement of the relay the spring arm 28 which supports the contact 21 is secured to the conducting supporting member 52 by means of a conducting bar 54 which is threadedly engaged by the screws 5|. A pair of conducting leads 55 and 56 which correspond respectively to the conducting leads 36 and 31 of Fig. 1 are sealed in a wall of the container l6 and extend therethrough, the conducting lead- 55 being electrically connected to the conducting support 52 and the conducting lead 56 being electrically connected to the cup-shaped member 48.

The circuit through the contacts 26 and 21 may be traced from the lead-in conductor 55 through the conducting support 52, the spring arm 28, the contacts 21 and 26, and the bimetallic element 22 to the supporting bolt II by way of a suitable conductor such as the conductor 23 shown in Fig. 1 and from the supporting bolt by way of the cup-shaped member 48 to the lead-in conductor 56. It will be seen that the conducting block 54 is threadedly engaged by a screw 51 which extends through the spring arm 28 similarly to the screw 32 in Fig. land is provided with an enlarged head 58 to form a stop for the contact 21.

Although relays embodying my invention may be used for various control purposes, the particular field of application lies in the protection of electrical energy translating apparatus such as motors or transformers. In order to be fully effective, the overload relay when so employed must have a thermal characteristic which corresponds to the effective thermal capacity of the protected apparatus.

As is well known, such apparatus may be considered in general as comprising magnetizable metallic parts, usually of iron, and conductor parts, usually of copper, electrically insulated from and thermally related to the iron parts. When such an apparatus is subjected to light overload conditions, the heat generated in the copper is conducted through the insulation to the iron wherebythe copper remains relatively cool,

but when the apparatus is subjected to heavy overload conditions, the copper is heated so rapidly that the heat cannot pass through the insulation to the iron quickly enough and consequently, the copper will reach dangerous temperatures while the iron remains comparatively cool. It will be seen from this that the eifective thermal capacity of such apparatus is proportional to the total weight of the copper and the iron under light overload conditions and is proportional to only the weight of the copper under heavy overload conditions. At intermediate loads the effective thermal capacity lies between the two extreme limits.

I have found that by properly proportioning the cross-section of the spirally wound portion l2 and the cup-shaped magnetizable members I3 and I4, the thickness of the cylindrical con ductor 20 and the length of the shoulder 2| which provides thermal contact between the conductor cylinder and the spirally wound portion l2, my relay can be constructed closely to follow the characteristic curve of a motor or transformer over a wide range of overload conditions. The cylindrical conductor 26, the magnetizable core structure of the relay and the degree of thermal conductivity therebetween provided by the shoulder 2| respectively represents the copper parts of the apparatus, the iron parts of the apparatus and the thermal relation therebetween.

In some cases the electric motor may be provided with auxiliary cooling means and in the usual transformer installations, the core and the windings of the transformer are immersed in a body of oil. It will of course be apparent that in either case, the effective thermal capacity of the apparatus will be considerably affected by the cooling means or by the immersing body of oil. This factor is taken care of in my improved thermal relay by enclosing the thermal operating parts of the relay within a sealed container, the degree of vacuum in the container being adjusted to give a degree of thermal conductivity between the thermal parts enclosed therein and the external ambient medium which corresponds to the thermal conductivity between the protected apparatus and the cooling means or the immersing body of oil.

Relays embodying my invention may be employed to protect energy translating apparatus of varying size and voltage, the only change which is necessary in order to adapt the relay to the particular rating and voltage of the apparatus being a change in the number of turns on the energizing winding 45. This energizing winding 45 is essentially the primary winding of a current transformer the secondary of which comprises the vacuum enclosed parts of the relay. This feature of my relay is very advantageous since it eliminates the necessity for current transformers which are usually resorted to for'supplying current to the ordinary type of thermal overload relay on high voltage installations.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A thermal relay comprising a primary winding, a closed circuited secondary winding disposed therewithin, a thermoresponsive device thermally associated with said secondary winding to be influenced by the heat generated therein and means including walls disposed within said primary winding enclosing said secondary winding and said thermo-responsive device for thermally isolating said enclosed elements.

2. A thermal relay comprising a primary winding, 2. single-turn secondary winding comprising a cylindrical conductor disposed within saidprimary winding, a thermo-responsive device thermally associated with said cylindrical conductor to be influenced by the heat generated therein, and means including walls disposed within said primary winding enclosing said cylindrical conductor and said thermo-responsive device for thermally isolating the same.

3. A thermal relay comprising a primary winding, a single-turn secondary winding comprising a cylindrical conductor disposed within said primary winding, a bimetallic element secured to said cylindrical conductor in heat-receiving relation therewith and means including walls disposed within said primary winding enclosing said cylindrical conductor and said bimetallic element for thermally isolating the same.

l. A thermal relay comprising a primary winding, a magnetizable core disposed within and spaced from said primary winding, a closed circuited secondary winding surrounding said core, a thermo-responsive device thermally associated with said secondary winding to be influenced by the heat generated therein and means including walls disposed within said primary winding enclosing said core, said secondary winding and said thermo-responsive device for thermally isolating the same.

5. A thermal relay comprising a primary winding, a magnetizable core disposed within and spaced from said primary winding, a singleturn secondary winding comprising a cylindrical conductor surrounding said core, a bimetallic element secured to said cylindrical conductor in heat-receiving relation therewith and means including walls disposed within said primary winding enclosing said core, said cylindrical conductor and said bimetallic element for thermally isolating the same. I

6. A thermal relay comprising a sealed container, an energizing winding adjacent an outer.

aoaisve.

7. A thermal relay comprising a sealed container, a primary winding disposed around said container, a single-turn secondary winding comprising a cylindrical conductor within said container in inductive relation with said primary winding, and a thermo-responsive device arranged in heat-receiving relation with said cylindrical conductor.

8. A thermal relay comprising an evacuated container, an energizing winding disposed around said container, a single-turn secondary winding comprising a cylindrical conductor within said container in inductive relation with said primary winding, and a bimetallic element secured to said cylindrical conductor to be influenced by heat conducted thereto from said cylindrical conductor.

9. A thermal relay comprising a sealed container, a magnetizable core within said container, a heating member comprising a cylindrical conductor surrounding said core, a thermo-responsive device in heat-receiving relation with said heating member, and means outside said container for producing a magnetic flux in said core to induce a heating current in said heating member.

10. A thermal relay comprising a sealed container, a magnetizable core within said container, a closed circuited heating winding surrounding said core, means including an energizing winding arranged outside said container for inducing a heating current in said heating winding, and a thermo-responsive device in heat-receiving relation with said heating winding.

11. A thermal relay comprising a sealed container, a magnetizable core supported within said container, a closed circuited heating winding surrounding said core, means including a magnetizable member arranged outside of said container having portions disposed adjacent the ends of said core for providing a low reluctance magnetic path between said ends, the walls of said container being interposed between said core and said adjacent portions of said magnetizable member, means including an energizing winding for producing a flux through said core and said magnetizable member whereby a current is induced in said closed circuited heating winding, and a thermo-responsive device within said container in heat-receiving relation with said closed circuited winding.

12. A thermal relay comprising a sealed container, a magnetizable core supported within said container, a heating member comprising a cylintions of said magnetizable member, means includ-- ing an energizing winding for producing a mag-- netic flux in said magnetizable member and said core to induce a current in said heating member, a bimetallic element within said container in heatreceiving relation with said heating member and circuit controlling contacts controlled by said bimetallic element.

13. A thermal relay comprising a frame of magnetizable material having aligned apertures in opposite sides thereof, a sealed container extending crosswise of said frame disposed in said apertures, a magnetizable core supported within said container with the opposite ends thereof adjacent said opposite sides of said frame, a closed circuited winding surrounding said core, means including an energizing winding for producing a magnetic flux in said frame and said core to induce a heating current in said closed circuited winding, and a thermo-responsive device within said container in heat-receiving relation with said closed circuited Winding.

14. A thermal relay comprising a frame of magnetizable material having aligned apertures in opposite sides thereof, a sealed container extending crosswise of said frame disposed in said apertures, a magnetizable core supported within said container with the opposite ends thereof adjacent said opposite sides of said frame, a heating member comprising a cylindrical conductor surrounding said core, means including an energizing winding for producing a magnetic flux in said frame and said core to induce a heating current in said heating member, a bimetallic element having one end fastened to said heating member to be heated by heat conducted therefrom and circuit controlling contacts controlled by the other end of said bimetallic member.

15. A thermal relay comprising a frame of magnetizable material having aligned apertures in opposite sides thereof, a sealed container extending crosswise of said frame disposed in said apertures, a magnetizable core supported within said container with the opposite ends thereof adjacent said opposite sides of said frame, a heating member comprising a cylindrical conductor surrounding said core, means including an energizing winding surrounding the portion of said container between said opposite frame sides for producing a, magnetic flux in said frame and said core to induce a heating current in said heating member, a bimetallic element secured to said heating member to be heated by conduction therefrom, and circuit controlling contacts controlled by said bimetallic member.

16. In a thermal relay comprising a sealed envelope, a magnetizable core structure therewithin comprising a rod supported axially of said envelope, spaced cup-shaped members supported on the opposite ends of said rod, and a spirally wound strip of magnetizable material surrounding said rod between said spaced cup-shaped members.

1'7. In a thermal relay comprising a sealed envelope, a magnetizable core structure therewithin comprising a rod extending axially of said envelope, spaced cup-shaped members carried by the opposite ends of said rod, a spirally wound strip of magnetizable material surrounding said rod between said cup-shaped members, means for supporting one end of said rod from a wall of said envelope, and means including a leaf-spring carried by one of said cup-shaped members for positioning the other end of said rod relative to said envelope.

18. A thermal relay comprising a sealed envelope, a magnetizable core structure therewithin comprising a rod supported axially of said envelope, spaced cup-shaped members supported on the opposite ends of said rod and a spirally wound strip of magnetic material surrounding said rod between said cup-shaped members, a closed circuited winding surrounding said spirally wound portion of said magnetizable core structure, a thermo-responsive device intimately thermally associated withsaid closed circuited winding and means for producing an alternating flux through said magnetizable core structure to induce a heating current in said closed circuited winding.

19. A protective device for electrical apparatus; said apparatus having metallic parts and electric conductors thermally related to the metallic parts, said device comprising a sealed container enclosing elements thermally cooperating to produce a. resultant thermal characteristic which substantially duplicates the thermal characteristic of the protected apparatus, one of said elements comprising a heat storage body of magnetizable material, another of said elements comprising a closed circuited winding thermally related to said magnetizable body, a thermo responsive device thermally associated with said closed circuited winding, and means for inducing a heating current in said closed circuited winding proportional to the current in the conductors of the protected apparatus, said magnetizable body, said closed circuited winding and said thermal relation therebetween being proportioned thermally to represent respectively the metallic parts of the apparatus to be protected, the conductors of said apparatus and the thermal relation therebetween, whereby said resultant thermal characteristic is produced.

20. A protective device for electrical apparatus, said apparatus having metallic parts, electric conductors thermally related to the metallic parts and cooling means for dissipating heat from the parts and the conductors, said device comprising an evacuated envelope enclosing elements thermally cooperating to produce a resultant thermal characteristic which substantially duplicates the thermal characteristic of the protected apparatus, one of said elements comprising a heat storage body of magnetizable material, another of said elements comprising a cylindrical conductor surrounding said magnetizable body, portions of said conductor and said magnetizable body being in direct heat-conducting engagement, a bimetallic element secured in heat-receiving relation to said cylindrical conductor, and means for inducing a heating current in said cylindrical conductor proportional to the current in the conductors of the protected apparatus, said magnetizable body, said cylindrical conductor and said thermally engaging portions thereof being proportioned thermally to represent respectively the metallic parts of the apparatus to be protected, the conductors of said apparatus and the thermal relation therebetween, the degree of vacuum within said sealed envelope being proportioned to duplicate the heatdissipating properties of said cooling means for the apparatus to be protected whereby said resultant thermal characteristic is produced.

BENJAMIN W. JONES. 

